Hello good sir. For everyone else on here, I apologize profusely if I give this guy a wrong answer. I just feel I have to contribute something instead of just asking questions!
Firstly, this game seems to be the only game I've ever seen that issues a warning only if you are over 18, and secondly the whole problem with the code is simply as Old Pedant already said, the spaces between the > and =. Change that and it should work.
EDIT: I'm assuming this is for some sort of learning exercise so I didn't attempt to try and 'improve' your code.